The present invention relates to a cooling device. More particularly, it relates to a cooling device which can be utilized by a consumer who needs to use low temperature at two or more temperature levels. For example it can be used for cooling of vegetable storage facility which needs high temperature cooling level from 0.degree. to -5.degree. C., low temperature cooling level for a freezer from -25.degree. C.--40.degree. C., and average temperature cooling level for a cooling chamber of the vegetable storage from -2.degree.--10.degree. C.
Freon compression cooling machines and installations are widely used for producing cold in the above mentioned temperature ranges. Such installations include a compressor for compressing a refrigerant, a condenser formed as a surface heat exchanger for cooling and condensing of the compressed refrigerant preferably due to thermal contact with cooling media such as atmospheric air or water, evaporator of the liquefied refrigerant at a low pressure corresponding to the pressure of compressor suction which determines the equilibrium temperature of boiling of the refrigerant and corresponding temperature of the object to be cooled (cooling chamber, space, etc.), and also throttling device for reducing the refrigerant pressure from the condensation pressure (pumping) to the evaporation pressure (suction). The throttling devices are usually formed as fixed local hydraulic resistances (such as for example portions of capillary pipes arranged in a line which connects the condenser with the evaporator), or regulatable hydraulic resistances which can be formed as throttle manual valve or driven throttle valves (thermo-regulating, electro-driven) in systems with automatic thermo-regulation of cooling area with the use of the circuits with a feedback and amplification. For cooling within the above mentioned temperature levels, unified compressor-condenser aggregates can be used as well as identical refrigerants, for example R 22. Differences in mode of operation and as a result different temperatures of boiling of refrigerant in evaporators are provided first of all by differences in hydraulic resistances of throttling devices, and secondly by different ratios of heat exchange surfaces of evaporators and objects to be cooled as well as thermal inflows into the systems. Most frequently in order to produce cold at different temperature levels separate cooling devices are utilized. This is not always convenient and advisable in view of technological and economical reasons, especially when the demand for low temperature level cold is not great and is needed only periodically.
The known system for cooling at two temperature levels contains, in addition to the joint compressor-condenser aggregate also a distributor of liquid refrigerant after the condenser, two evaporators with different cooling chambers, and a collector connecting the flows of refrigerant vapors after the evaporators before their return to the compressor suction. An additional hydraulic resistance is arranged in the return line of vapors from the evaporator of high temperature chamber between the exit from the evaporator and the collector. Thereby the pressure in this evaporator is established at the higher level than the suction level and the corresponding pressure in the low temperature evaporator. Therefore the temperature of refrigerant boiling in the evaporator with the additional throttling device at the exit from it is established at the higher level. An increase in the value of hydraulic resistance of the additional throttle leads to the proportional increase of the pressure jump at it and the temperature increase in the corresponding section of the cooling device. The distributor of the liquid refrigerant separates its flow for parallel evaporators proportionally to the cooling efficiency at each temperature level. The disadvantage of this circuit is its low energy efficiency due to high thermo-dynamic irreversibility of processes in the branch with the additional throttle. The result of this irreversibility is low technological and economical characteristics of the system as a whole. The compressor compresses the whole flow of refrigerant in the pressure intervals corresponding to the temperature differential required for producing the low temperature cooling, and this differential and pressure corresponding to it is used only in one section. The efficiency of such systems is especially low when the demand for low level cooling with respect to the quantity of high level cooling is low. In practice such ratios are more probable. For example, cooling efficiency of devices at the refrigerant boiling temperature 0.degree. to 10.degree. C. can exceed the cooling efficiency of freezers 10-30 times. Therefore, it is considered to be inefficient to combine in a single device of cascadeless type (with one stage compressor) the functions of generation of cooling with high and low levels. The second reason of difficulties to provide efficient systems of this type is uncorrelating schedules of demands for cooling at different temperature levels. The cascade multi-compressor cooling devices used in praxis for producing cooling at two or more temperature levels are complicated, cumbersome, expensive, and their reliability is relatively low.
A substantial disadvantage of cooling device which generate cooling at the level of -5.degree.--50.degree. C. and used for storage of some wet products (for example bulk meat, fish, vegetables, etc.), as well as for air cooling below 0.degree. C., is freezing of ice and frost layer on heat exchanging surfaces of evaporators. Frost thermally insulates the surfaces of the heat exchanger ribs, reduces the heat exchanging surface and leads to the reduction of cooling efficiency, increases electrical energy consumption, reduction of suction pressure and increase of compression degree of the compressor, its overheating and excessive wear if melting is performed not sufficiently frequently. The process of melting is time consuming, and during the melting period the cooling chamber is subjected to undesirable heating. Cold accumulated by deposits of ice and frost not only is not used, but additional energy is wasted for its removal. During the use of heated vapors of compressed refrigerant for heating and melting the compressor operates idly.
Existing constructions for cooling such objects as standard cans and containers for beverages also have substantial disadvantages which make difficult or impossible the task of fast cooling to the level of environmental temperature. Known coolers are usually cooling chambers with the interior temperature of -5.degree.--30.degree. C.
Heat withdrawal from the objects is performed through passive, little movable air layer. The main mechanism of heat transfer is a natural air convection. For these conditions very low heat exchange efficiency is available. The level of frost on the surface of the evaporator additionally worsens the heat exchange. Masses and sizes of elements on equipment to be cooled are many times higher than the sizes of objects to be cooled, the walls of cooling chamber are cooled faster to minimal temperatures than the objects to be cooled, and despite the high thickness of thermal insulation, cooling losses exceed the cold which is used efficiently while the time of cooling reaches hours. The same reasons make difficult the preparation of small quantities of food ice as well as accumulation of cold in small autonomous mobile isotherming storage chambers. The absence of control of current temperature of the objects to be cooled directly leads to substantial deviations of real temperature from the given magnitude.